Ultra high frequency power measuring device



Sept. 24, 1946. '.1. w. coLTMAN 2,408,198

ULTRA HIGH-FREQUENCY POWER MEASUR'ING DEVICE v vF11-ed Fei. 5, 1945 Jolm 001mm.

Patented Sept. 24, 1946 ULTRA HIGH FREQUENCY POWER MEASURING DEVICE John W. Coltman, Forest Hills, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania f Application February 5, 1943, Serial No. 474,884

This invention and discovery relates to a method and device for measuring ultra highfrequency power, and has particular relation to apparatus for vmeasuring the ultra high-frequency power delivered from a wave guide.

In accordance with prior. art practices, ultra high-'frequency lpower is measured by absorbing the energy in water and measuring the resulting increase in temperature of the water. rllhe power output. of an ultra high-frequency generator is oftenV measured in this way. The wave guide is disconnected from the load adjacentfrtoV the generator and a cap is mounted over the open end of the .wave guide.. The cap includes a quartz.

plate extending directly across the waveguide opening and the remainder ofv the vcap cooperates with the quartz plate to form a small chamber immediately above the plate. A water reservoir, pump. 'and :conduits are then arranged to pass a constantstream of water through the chamber. The position and form ofthe plate and chamber are such as to permit all ofthe energy incident to the plate to be absorbed in the water. Knowing the rate of iiow of the waterV and the temperature of the y,water before'and after it,v passes throughthechamber, the average power may be calculated.

The water temperature arrangement. for determiningthe power gives good results but also has certainobjectionable features. The apparatus is quite bulky and requires not only a water supply but certain supplementary equipment, including pumps, conduits,Y valves, and .sensitive galvanometers. Consequently, it is impractical for use in the eld and inconvenient to handle in the laboratory. In addition, the-,apparatus cannot show an erratic supply from the source because there is a time lag in the response of the. water temperature as A indicated on the rvgalvanometers, to changes in the source. If tuning operationsare carried out to vary the output of the source, an appreciable time mustelapse, because of the slow response in the indicated water temperature, beforel the eiect of the tuning operations on the output cans-be determined. Moreover, the arrangement enables comparatively easy calculation of the average powerbut the Vduty cycle must be'lmown to calculate the peak power. Other difliculties encountered in theuse of the water temperature arrangement involve the control of the rate of .water iiow and the positioning of (the cap on the end of vthe wave guide.V y f rA relatively quick estimate of the power being delivered from a wave guide may be madeby. placing an ordinary neon bulb over the output 18 Claims. (Cl. 171-95) end of theguiae, causing the buib 1.0 glow. The brightness of the glow produced in the bulb is an indication of the strength vof the eld producl ing the ionization of the neon-gas. However, the

. by reflection from nearby objects.

' use of a neon lbulb Aenables only a very rough estimate of the power to be made for the visual impression of brightness is extremely diiicultto retain. *Moreover, the glow'in a neon bulb is violently'affected by slight changes in the neighboring electric eld, such as might be introduced It istherefore, an object of my invention to provide a simple and inexpensive device for measuring ultra high-frequency power. .'It is`another object of my invention to .provide novel apparatus for measuring ultra highfrequency power which enables a direct, instantaneous and accurate .reading of the power to -be made.

AA further object of my invention is to provide a new and improved method of measuring ultra high-frequency power.

n It is still another object of my invention to provideY a novel methodA and apparatus for measuring the ultra. high-frequency power delivered' from a wave guide. Y

Another object 'of my invention is to provide a novel'device for measuring ultra high-frequency peakpower.

vIt is a further'object of my invention to provide a simplified device for measuring ultra highfrequency power which is not affected by slight changes in theY neighboring electric field. y Y More specifically, it is an object of my invention to provideY a compact, portable device for measuring ultra high-frequency power which does 'not Vrequire any supplementary apparatus or supply sources.

'.My invention arises from the discovery that upon introduction of an electric eld into an insulated column of gas at a selected point thereon with the column of a capillary cross-sectional area and the gas of the type which produces a visible'glow in the presence of an electric eld measure of; the intensity of the electric eld which isl introduced. into the column and of the power absorbed thereby.

My discovery may be advantageously employed Vin the'provision of. a' measuring device comprising an (elongated envelope of translucent in- 1 sulating material having a capillary bore therein lled with neon or other gas which produces a glow in the presence of an electric neld of a predetermined intensity. The device is adapted to have the electric field to` be measured introduced at a selected point in the capillary bore. If the intensity of the introduced field is suinciently great, the gas is ionized at the `point of introduction and acts as a partial conductor along which the field travels.

As the field travels along the column of ionized gas contained within the capillary bore, its energy is dissipated in ionizing the gas, losses in. the material of which the envelope is formed, and in radiation. When the neld intensity decreases. below the critical value necessary toionize the gas, the glow ceases at that point. Thus a column of glowing gas extends along the capillary bore from the selected point for a distancev depending upon the original intensity of the eld introduced into the capillary bore and the distance is a measure of the power absorbed by the device. l t has been discovered that the glow diminishes slightly in brightness along the capillary bore but that it comes to a termination very suddenly. Moreover, it hasv been discovered that slight changes in neighboring electric fields as might be caused by wave reflections, do not affect the length of the glowing column. A calibrated scale may be placed along the capillary bore to give a direct reading of the intensity of the elec'- tric field introduced in thebore o r the power absorbed by the device.

The electric fieldmay be introduced into the capillary bore in various Ways. A satisfactory way-is to provi-de a small' exciting chamber at one end of the bore of larger diameter bul-I considerably shorterin length than the bore, This chamber is also lled with gas and is adapted to be positioned to be exposed to the electric neld to be measured; The field then, ionizes the gas in the chamber' which acts as a partial conductor to introduce the electric neld into the bore. Other arrangements for introducing the eld into the bore may also be employed advantageously such as the use of' a conducting electrode or electrodes exposed to the electriceld. It has'alsoY been discovered that anV electric yeld of high intensity may be introduced into the capillary bore by merely placing a portion thereof directly in the path of the energy. An'exciting chamber isv preferable, however, because the increased relation between the volume of the gas and the area of the surface within which it is contained greatly facilitates the original'ionization of the gas.

Although the intensity of any ultrahigh-frequency electric field may be measuredv by this new method, apparatus is provided in accordancel with my invention for measuring power in. systems in which the power is transmitted through hollow wave guides. As the length of the column of glowing gas in the envelope` is a measure of the p ower absorbed thereby, it is apparent that if a known percentage of the power in a wave guide is diverted into the capillary bore of the envelope, a power reading may be taken.

A simple way of diverting a known percentage of power from a wave guide into the capillary bore of'anenvel'ope is to divert all of the power. The wave guide may be disconnected from the load anda small additional section of wave guide connected thereto. A tting is provided to mount the envelope on the wave guide section with the exciting chamber or electrode extending into the wave guidev so that it is` exposed to the electric field in the guide, A snorting stub is, then inlli 4 serted in the output end of the guide section and adjusted to eliminate wave reflections so that all the power is diverted into the capillary bore of the envelope.

It then becomes apparent that the same calibrated measuring apparatus may be employed in different systems of the same frequency and wave length. It is compact, portable and inexpensive. In addition it may be conveniently employed in the field and enables an instantaneous reading of the peak'power.

The. features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as toits organization and its method of operation together with additional objects and advantages thereof viull best be understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which:

Figure 1 is a View of the preferred embodiment of the measuring device,

Fig, 2 illustrates an arrangement for measuring the power in a system using a wave guide, and

Figs. 3, 4 and 5 illustrate various arrangements for introducing the electric eld into the capillary column of gas.

As shown in Fig. l, the preferred embodiment of the measuring device consists of an elongated envelope 3 of glass or other translucent insulating material. The envelope 3 has therein a capillary bore 5 extending from a reservoir 1 at one end to a small exciting chamber 9 at the other end. The chamber 9 is of slightly larger cross sectional area than the capillary bore 5 but is considerably shorter in length. The capillary bore 5, reservoir 'l and' chamber 9 are filled with neon or other gas of the type which produces a glow in the presence of an electric eld of a predetermined intensity. y

The envelope 3 is adapted to be positioned with the chamber 9 exposed tothe electric field to be measured. The` eld causes the gas in the chamber to be ionized forming a partial conductor for the electric field to introduce it into the end of the capillary bore 5. The gas at the end of the capillary bore is ionized by the electric eld which is introduced therein and the ionized gas conducts the neld along the capillary bore. As .the field is conducted along the bore, it dissipates itsV energy and the intensity of the field decreases gradually as it is conducted along the capillary bore until it falls below the critical value necessary to maintain ionization of the gas. The length of the capillary bore is such that the eld intensity drops below the critical value intermediate the ends of the bore. Thus the eld causes only a portion of the gas in the capillary bore to produce a glow, there being a sharp line of demarcation between the ionized or glowing, gas andthe non-glowing gas. A calibrated scale l l` extends along. the capillary bore 5 to facilitater measuring the length of the glowingy column and to give a direct reading of the power absorbed by the device.

The reservoir 1 is used to replace gas losses and insure anadeduatesupply of gas' in theV capillary bore andv thereby extend the life of the device. However, the reservoir isy not essential to the operation of the device.

In Fig; 2, a wave guide I3 supplied from a source4 of ultra high-frequency power is shown in crosssection with an open-ing l9` in'.a wall of the guide which isA normal tdtheelectric field createdl in the guide when power is supplied thereto, the direction of the yiield being indicated by an arrow 20.l The opening I9 is surroundedby an inter-f nally threaded boss 2| mounted on the outside ofl the guide. v The glass tube or envelope 3a with the capillary bore 5 is similar to envelope 3 in Fig. 1 but does not have a reservoir and has a member 23 cementedabout the end thereof adjacent to the chamber 9. The member 23 is threaded to screw into the boss 2|, and support envelope 3a. with the chamber 9 within the wave guide, as shown, exposed to the electric field in the guide. YA nut` 25 is then employed to hold the member 2 3 in thedesired position.- A shorting vstub 23 is provided in the output end of the wave guide. lThis stub, may be of any suitable shape, there being various designs in use at present, and serves to createl a short circuit across the end of the guide. The position of the` stub is adjustable so that byproper adjustment of thestub 26 andthe position of the exciting chamber 9, wave reflections may be eliminated so that substantially al1 of the power is diverted into the capillary bore. HI have discovered that the wave reilections may be eliminated more-readily if the exciting chamberof the envelopeis inserted through a wall of the guide whichis normal to the electricreld Ain the guide.

In Fig.v 3 is illustrated a device having the chamber 9 of Fig. 2 replaced byra conducting electrode 27. The envelope 3b is mounted on a wave guide in the manner described in Fig. 2 with the electro-de 2l extending from the bore 5 into the guide. The electrode 21 then serves to `introducelthe electric eld into the end of the capillary bore 5.

In Fig. 4 is illustrated an arrangement for introducing the electric-field into the capillary bore from a coaxial 4transmission line 2S. The lenvelope 3b its mounted on the outer conductor of the-coaxial line similarly to the mounting of the envelope onthe wave guide in Fig. 3, but the conducting electrode 21 in the end ofthe capillary bore `5 is connected to the center conductor 3l of the coaxial line. -AA shorting stub 33 is employedto direct substantially all of the power into the'capillary bore; ,Y i

. In measuring power above a predetermined magnitude the use of an igniting chamber or electrode ymay be avoided. In'such a situation, a capillary tube 3c sealed at both ends and lled with gas will be effective if a portion of the tube itself is placed across the wave guide as shown invFig. 5. Of course, if the tube 3c extends on both sides of the guide, the glowingcolumn also extends on both sides. If desired, the tube 3c may' extend through the guide intermediate the ends and a snorting stub employed.

It is Yto be noted that a capillary bore must be employed to support the gas column. If a large bore is used, the glow tends to follow the surface of the bore producing glowing fingers and the line between glowing and non-glowing gas is extremely irregular and quite shadowy.

In ultra high-frequency systems using a wave length of 3 centimeters, I have found a bore of approximately 3 millimeters or less in diameter is satisfactory with a diameter of .5 millimeter preferred. Neon gas is also preferred at a pressure of approximately '7 millimeters. The device may be calibrated in kilowatts with a peak power d of 5 kilowatts giving a glowing column over ten centimeters in length with a .5 millimeter bore.

Although I have shown and described a preferred embodiment of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and the spirit of the appended claims.

I claim as my invention:

1. A device for measuring the intensity of an ultra high-frequency electric field comprising an elcngated'envelopeof translucent, insulating material having a capillary bore therein lled with gas of the type Which produces a glow in the presence of an electrici'ield of a predetermined intensity, said envelope being adapted to have the electric eld to be measured introduced into said bore at a selectedplace whereby said field travels alo-ng said bore from said place, said bore being of such length that said eld decreases below said predetermined intensity intermediate the ends of the bore.

2. A device for measuring the intensityof an ultra, high-frequencyv electric eld comprising an elongated envelope of translucent, insulating material having a capillary ibore therein lled with gas of the type which produces a glow in the presence of an electric iield of a predetermined intensity, said envelope being adapted to have the electric iield to be measured introduced into said bore at a selected place whereby said eld travels along said bore from said place, said bore being 0f such length that said field decreases below said predetermined intensity intermediate the ends of the bore, and a calibrated scale extending along said bore.

3. A device `for measuring the intensity of an ultra high-frequency electric i-leld comprising an elongated envelope of translucent, insulating materialhaving a capillary bore thereinlled with gas of the typeA which produces a glow in the presence of an electric eld above-a predetermined intensity and exciting means yassociated with said bore which is effective when exposed to an electric eld ,to introduce that field into vsaid bore at aY selected place whereby said field travels along said :bore from said place, said bore being of such length that said field; decreases below said predetermined intensity intermediate the ends of the bore.

4. A device for measuring the `intensity of an ultra high-frequency electric eld comprising an elongated envelope of translucent, insulatingmaterial having a capillary `bore therein filled with gas `of the type which produces a glow in Athe presence of an electric field above a. predetermined intensity, means` associated with said bore for introducing the electric eld to be measured into said bore at a selected point whereby said field travels along said bore from said point, said bore being'ofsuch length that said eld decreases below said predetermined intensity intermediate the ends of the bore, and al calibrated scale extending along said bore. Y

5. A device for measuring the intensity of an ultra high-frequency electric eld comprising an elongated capillary tube of translucent, insulating material, sealed at :both ends and lled with gas of the type which produces a glow in the presence of an electric field of a predetermined intensity.

6. A device for measuring the intensity of an ultra high-frequency electric field comprising an elongated capillary tube of translucent, insulating ultra high-frequency electric field comprising an 7 elongated capillary tubelof translucent,v insulating material, said tube` having a bore of a diameter of the` order of .5- to 3 millimeters, sealed at both ends andy filled with gas of the type. which produces a glow in the presence of an electric ield of a, predetermined intensity.

8.. A device for measuring the intensityA of an ultralhi'gh-frequency electric eld comprising an elongatedenvelope of translucent, insulating materialY having therein an exciting chamber at one endl andy a reservoir at'the other end and a capillary bore interconnecting said chamber and reservoir, said chamber, reservoir and bore being filled with gas of the type which` produces a glow inthe presencelof an electric field of a predetermined intensity.

9L A device for measuring thev intensity of an ultra high-frequency electric eld comprising an elongated envelope of translucent, insulating material having therein an excitingl chamber atA one end and a reservoir at the other end and a capillary bore of a diameter of the order of .5 to 3.0 millimeters interconnecting said chamber and reservoir, said chamber, reservoir and bore being filled with gas ot the type which produces a glow in the presence of an electric eld of a predetermined intensity.

10. A device for measuring the intensity of an ultra high-frequency electric field comprising an elongated envelope of translucent, insulating material having therein an exciting chamber at one end and a reservoir at the other end and' a` capillary boreinterconnecting said chamber and reservoir, said chamber, .reservoir and bore being filled with gasA of the type Whichproduces a glowin the presence ofV an electric eld 0f a predetermined intensity, anda calibrated scale extending along said bore.

ll. A device for measuring the intensity of an ultra high-frequency electric field comprising an elongated envelopeof translucent, insulating material having a capillary bore therein filled with gas of the type which produces a glow inthe presence of lan electric leld` of a predetermined intensity, andconducting electrode means ex tending into said bore at a selectedk point.

12. A device for measuring thein-tensity of yan ultra high-frequency electric field comprising anelongatedv envelope of' translucent, insulatingmaterial having a capillary bore therein of a diam- I eter of the order ofl .5to 3 millimeters filled with gas of the type which produ-ces a gloW in the presencevof an electriceld oi a predetermined intensity, and conducting electrode means exten-ding into said bore at a` selected point.

13. A device' for measuring the intensityof an ultra high-frequency elec-tric eld comprising an elongated envelope of "translucent, insulating material having therein abore ofy adiameter of the order of .5 to 3.0i millimeters filled with gas ef the type which produces aglow in the presence of an electric eld above a predetermined intensity, exciting means associated with sai-dbore for introducing the electric eld to be measured intoV said bore at a selected point' whereby said field travels along said borefrom said point, and a scale extending alongsaid bore.

14. A device for measuringthe intensity of an ultra high-frequency electric field comprising an elongated envelope of translucent', insulating material having therein a bore'- of a diameter' of the order of .5 to 3.0 millimetersy lled withgas of the .type which produces a glow in the presence of an electric 'eld above a predetermined intensity, and exciting means associated with said bore for introducing the electric' eldf to be measuredV into said bore at a selected poi-rit 1'5. A device for measuring the intensityV ofV an ultra high-frequency'electric e'ld comprising an elongated envelope of translucent', insulating material having thereinv an exciting' chamberr and a capillary bore opening i'nt'o said: chamber with said bore .andi chamber being filled withA gas of the type which produces a glow in the presence of an electric field of apredetermined intensity.

16. A device for measuring the intensity of an ultrahigh-frequency electric eld comprising an elongated envelope of translucent, insulating material having therein an exciting chamber and a capillary bore opening into said chamber, said bore and chamber being lled with gasof the type which produces a glow` in the presence of an electric field of a predetermined intensity, and a scale extending along said bore.

117'. A device for measuring the intensity of an ultra high-frequency electric field comprising an elongated envelope oftranslucent, insulating material having therein anl exciting chamber andy a bore of a diameterr of the order of .5 to 320 millimeters opening into said chamber, said bore and chamberV being lled with gasof the type which producesa glow in' the presence of' an electric' field of a predetermined intensity.

19;; A device for measuring-the intensity' of-r anul'tra high-frequency electric-lleid-1 comprising anelongated envelope of 'translucent insulating m-aterial having' a capillary bore'- therein filled with gas oi the type which produces`V a glow inthe presence of an electric eld abovea predetermined intensity; conducting electrodernea-ns' ex tending' into saidY bo-refor introducing the elec--` tric field to be measured intovsaid bore ata' sev lected' point-whereby said field travels along said bore from said-point and a scale extending along said bore.

J @HNi W2 COLT-MAN. 

